The present invention relates generally to electromagnetic door locking devices and more particularly to shear locks having improved features which ensure that the lock operates rapidly and positively during both locking and unlocking operations.
Various types of electromagnetic door locks are known. One type commonly referred to as a shear lock comprises an electromagnet mounted to or in a frame defining a doorway. An armature is movably mounted to travel with a door as the door moves in the doorway between an "open" and "closed" position. When the door is in the closed position, the armature is positioned in spaced relation from the electromagnet, but is mounted to or in the door such that when power is applied to the electromagnet the armature responds to the magnetic field and becomes engaged on an adjacent surface of the electromagnet.
Various styles and types of shoulder means such as ledges, tangs, and tabs have been employed to provide some physical interrelationship between the face of the electromagnet and the armature to enhance the lock's resistance to a shearing movement which would result from any attempt to open the door while power was applied to the electromagnet. It has been observed that such shoulder means exhibit increasing wear and potentially decreasing performance with time, thus mandating replacement of the shoulder elements exhibiting such wear. Where the shoulder elements are integral with the major elements of the electromagnetic lock, such replacement can be quite costly.
It would therefore be desirable to provide such shoulder means in the form of easily replaced, separate, low cost elements. Preferably, such replaceable elements are constructed to have material hardness less than the material hardness of the elements with which they cooperate to achieve the desired physical shear-inhibiting interrelationship. This selection of lesser material hardness results in reduced wear on the cooperating element thereby extending the life of the lock as a whole.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.